Control valve

ABSTRACT

A pressure compensating element ( 8 ) for a control valve ( 3 ) for controlling an overflow of a medium from a first pressure space ( 1 ) into a second pressure space ( 2 ) has a diaphragm ( 9 ) separating the pressure spaces ( 1, 2 ) from one another. The pressure compensating element ( 8 ) compensates forces acting on a valve body ( 5 ) of the control valve ( 3 ) and generated by pressure differences in the pressure spaces ( 1, 2 ). However, an overflow of a medium from one pressure space ( 1 ) into the other pressure space ( 2 ) takes place solely in the region of the control valve ( 3 ).

[0001] The invention relates to a control valve for controlling anoverflow of a medium from a first pressure space into a second pressurespace having a pressure different from a pressure in the first pressurespace, with a valve body prestressed against a valve seat, with acontrol device for moving the valve body and with a movable pressurecompensating element which is subjected to the pressure differencebetween the pressure spaces and is connected to the valve body and whichis intended for compensating the pressure forces acting on the valvebody.

[0002] Such electromagnetic control valves are used, for example, indevices for exhaust-gas recirculation in internal combustion engines ofpresent-day motor vehicles. In this case, the pressure spaces take theforms of the intake duct and the exhaust duct of the internal combustionengine. In such devices for exhaust-gas recirculation, a part stream ofexhaust gas is branched off from the exhaust duct and is supplied to theintake duct. The nitrogen fraction in the exhaust gas can thereby bereduced. The ratio of the exhaust-gas quantity to be supplied to thefresh-air quantity depends on, for example, the load state, thetemperatures or the rotational speed of the internal combustion engineand is determined by the control of the valve body. For this control,the control device has, for example, a pneumatic, electromagnetic orelectromotive actuating drive.

[0003] In order to avoid particularly high actuating forces during themovement of the valve body when there are high pressure differencesbetween the pressure spaces, a control valve has become known frompractice, in which a second valve body is designed as a pressurecompensating element. The valve bodies are fastened on a common valveshaft and, in the basic position, in each case bear on a valve seat. Oneof the pressure spaces is connected to the region between the valvebodies, whilst the regions on those sides of the valve bodies which faceaway from one another are connected to the other pressure space. As aresult, forces generated due to pressure differences in the pressurespaces act in each case on the valve shaft, but in opposite directionsof force.

[0004] A disadvantage of the known control valve is that the respectivedistances between the valve bodies and the valve seats must haveparticularly low tolerances. Moreover, for example, in the event ofthermal expansion of the valve shaft or wear of the valve bodies and ofthe valve seats, the control valve does not reliably seal off thepressure spaces from one another. Different expansions of the valvebodies and the valve seats likewise result in leaks.

[0005] The problem on which the invention is based is to design acontrol valve of the type initially mentioned, in such a way that itdoes not need low tolerances and reliably seals off the pressure spacesrelative to one another.

[0006] This problem is solved, according to the invention, in that thepressure spaces are sealed off relative to one another in the region ofthe pressure compensating element.

[0007] By virtue of this design, the control valve according to theinvention has a single valve body. The valve body and the pressurecompensating element are separated from one another as result of theinvention. The control valve according to the invention therefore doesnot need to have particularly low tolerances. A leak in the controlvalve according to the invention can consequently be avoided in a simpleway. The control valve according to the invention is therefore suitable,in particular, for use in a device for exhaust-gas recirculation in aninternal combustion engine of a motor vehicle.

[0008] The pressure compensating element could, for example, be a pistondisplaceable in a cylinder arranged between the pressure spaces.According to another advantageous development of the invention, thepressure compensating element reliably seals off the two pressure spacesrelative to one another if the pressure compensating element has adiaphragm for separating the pressure spaces.

[0009] According to another advantageous development of the invention,the pressure compensating element has a particularly simple constructionif a valve shaft designed for adjusting the valve body is connected to adisk holding the diaphragm.

[0010] According to another advantageous development of the invention,disturbances of the pressure compensating element which are generated byflows within the pressure spaces can reliably be avoided if the pressurecompensating element is designed to subdivide a container into twochambers, and if the first chamber is connected to the first pressurespace and the second chamber to the second pressure space.

[0011] The control valve according to the invention has a particularlycompact design if the container is arranged on that side of the firstpressure space which is located opposite the second pressure space, andif a pressure compensating duct is designed to connect the secondpressure space to the second chamber.

[0012] When the control valve according to the invention is in the basicposition, particularly reliable sealing off of the pressure spaces canbe ensured in a simple way if the valve body is capable of beingreturned into the closing position by means of a spring element. Thespring element may be manufactured, for example, from spring steel.Since the spring element has to transmit only very low return forces, itmay also consist of a metal memory alloy.

[0013] According to another advantageous development of the invention,an equilibrium of the forces acting on the valve body and on thepressure compensating element can be established in a simple way if alever is arranged between the valve body and the pressure compensatingelement.

[0014] The invention permits numerous embodiments. In order to make itsbasic principle even clearer, three of these are illustrated in thedrawing and are described below. In the drawing:

[0015]FIG. 1 shows a sectional illustration through a first embodimentof a control valve according to the invention in longitudinal section,

[0016]FIG. 2 shows a further embodiment of the control valve accordingto the invention in longitudinal section,

[0017]FIG. 3 shows a diagrammatic illustration of a further embodimentof the control valve according to the invention.

[0018]FIG. 1 shows in longitudinal section a device for exhaust-gasrecirculation in an internal combustion engine of a motor vehicle, witha first pressure space 1 taking the form of the exhaust duct and with asecond pressure space 2 taking the form of the intake duct. A controlvalve 3 allows an overflow of exhaust gas from the first pressure space1 into the second pressure space 2. The control valve 3 has a valve body5 bearing on a valve seat 4 and a control device 6 for moving the valvebody 5 perpendicularly to the valve seat 4. The valve body 5 isconnected to the control device 6 via a valve shaft 7. The controldevice 6 can adjust the valve shaft 7, for example by means of anelectromagnet which is not illustrated. Consequently, for exampledepending on the rotational speed of the internal combustion engine, onthe load state or on the temperatures, a connection of the pressurespace 1 taking the form of the exhaust duct to the pressure space 2taking the form of the intake duct can be made and exhaust gas can bemixed with fresh air.

[0019] A pressure compensating element 8 with a disk 10 holding adiaphragm 9 is fastened to the valve shaft 7. The disk 10 is prestresseddownward by a spring element 11 designed as a helical spring. Thediaphragm 9 is arranged in a container 12 and subdivides the latter intotwo chambers 13, 14. The diaphragm 9 allows movement of the disk 10 andconsequently of the valve shaft 7 and separates the media flowing in thepressure spaces 1, 2. The first chamber 13 is connected to the firstpressure space 1 and the second chamber 14 is connected, via a pressurecompensating duct 15, to the second pressure space 2. The pressurecompensating element 8 has essentially the same cross-sectional area asthe valve body 5, so that a pressure difference between the chambers 13,14 and consequently between the pressure spaces 1, 2 introduces, via thepressure compensating element 8, the same forces into the valve shaft 7as the valve body 5. In this case, the forces point in oppositedirections and therefore cancel one another out. For the sake ofclarity, the forces acting on the valve body 5 and on the disk 10 areidentified by arrows in the drawing for the situation where a lowerpressure prevails in the first pressure space 1 than in the secondpressure space 2. The spring element 11 serves as a return element forholding the valve body 5 on the valve seat 4 when the control device 6is under no force. Since the forces acting on the valve body 5 due tothe pressure difference between the pressure spaces are compensated bythe pressure compensating element 8, the spring element 11 can have alow spring force and a particularly flat spring characteristic.

[0020]FIG. 2 shows a further embodiment of the control valve. Here, apart region of the first pressure space 1 is surrounded by a secondpressure space 2 having a C-shaped cross section. A valve body 16 and apressure compensating element 17 are arranged in the legs of the secondpressure space 2. The pressure compensating element 17 has a disk 19fastened to a valve shaft 18 and a diaphragm 20 fastened to the disk 19.The valve body 16 is likewise fastened to the valve shaft 18 and, in theposition depicted, bears on a valve seat 21. When the valve body 16 isin this position, the media flowing in the pressure spaces 1, 2 areseparated from one another. As in the case of the control valve fromFIG. 1, forces acting on the valve shaft 18 and generated due to apressure difference in the pressure spaces 1, 2 cancel one another out.

[0021]FIG. 3 shows diagrammatically a further embodiment of the controlvalve. Here, the pressure spaces 1, 2 take the form of ducts arrangedparallel to one another. The control valve has a valve shaft 23displaceable by a control device 22 and a valve body 24 fastened on thevalve shaft 23. In the position depicted, the valve body 24 isprestressed against a valve seat 25. A lever 28 engages on the valveshaft 23. The lever 28 is mounted pivotably about a fixed bearing 27 andconnects the valve shaft 23 to a pressure compensating element 26. Thepressure compensating element 26 has a disk 29 which is articulated onthe lever 28 and which is held in an orifice 31 by means of a diaphragm30. The diaphragm 30 seals off the orifice 31 relative to the disk 29.

1. A control valve for controlling an overflow of a medium from a firstpressure space into a second pressure space having a pressure differingfrom a pressure in the first pressure space, with a valve bodyprestressed against a valve seat, with a control device for moving thevalve body and with a movable pressure compensating element which issubjected to the pressure difference between the pressure spaces and isconnected to the valve body and which is intended for compensating thepressure forces acting on the valve body, wherein the pressure spaces(1, 2) are sealed off relative to one another in the region of thepressure compensating element (8, 17, 26).
 2. The control valve asclaimed in claim 1 , wherein the pressure compensating element (8, 17,26) has a diaphragm (9, 20, 30) for separating the pressure spaces (1,2).
 3. The control valve as claimed in claim 1 or 2 , wherein a valveshaft (7, 18, 23) designed for adjusting the valve body (5, 16, 24) isconnected to a disk (10, 19, 29) holding the diaphragm (9, 20, 30). 4.The control valve as claimed in at least one of the preceding claims,wherein the pressure compensating element (8) is designed to subdivide acontainer (12) into two chambers (13, 14), and the first chamber (13) isconnected to the first pressure space (1) and the second chamber (14) tothe second pressure space (2).
 5. The control valve as claimed in atleast one of the preceding claims, wherein the container (12) isarranged on that side of the first pressure space (1)